Update git submodules

Update git submodules

* Update docs/submodules/fuel from branch 'master'
  - Merge "lib.sh: Reuse /tmp/mcp.rsa if present"
  - lib.sh: Reuse /tmp/mcp.rsa if present

    Long-term, /tmp/mcp.rsa should be moved to a persistent location [1],
    and made configurable via env var / other mechanisms.
    This will allow us to:
    - use an existing keypair (provided by end-user in expected path);
    - login to previous deployment machines (e.g. to cleanup UEFI boot
      entries before destroying the cluster and rebuilding it);
    - split deploy in re-entrant stages (salt master only, cluster nodes
      only; similar to old Fuel, where we could reuse old Fuel VM);

    [1] https://jira.opnfv.org/browse/FUEL-280

    Change-Id: I1e53321ed1cfc217ff95e809c867fa3370c479c9
    Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>